Sound recording system



SOUND RECORDING SYSTEM Filed March 18, 1929 m- ....mnn.

DDD

[nwzor Pag JPam gray.

Patented nec.- 29, 1931 UNITED. STATES Pix'rlazla'rl OFFICE ROYJ. POMEROY, F LOS .ANGIEEES, CALIFORNIA.

SOUND RECORDING SYSTEM,

Appueatign mea maren 1s,

La;l the present invention is well adapted to prodistorted reproduction.

duce the present known variable width record having a single serrated edge, the preferred form of the invention produces a varable width record having a double serrated e ge. i

The variable width type of record has certain well recognized advantages over the variable density'type. Among these may be mentioned, first, that both the negativeand positive variable width records are suitable recordsfor reproduction; while, as is well known, a negative of the variable density type is not suitable for reproduction, only the positive being a true sound record. And, second, a serious and diiiicult problem exists in making the variable density record of an exactly proper density and contrast for un- Obviously, this problem does not exist in the processing bf variable width records.

The present invention provides a method and system for producing a variable width record, for instance, with the use of the well known light valve embodying a current carrying loop of metallic ribbon strung in a magnetic Iield longitudinally over a rectangular light aperture, and electro-magnetically vibrate'd transversely of the light aperture to control the quantity of light passing therethrough. This light valve was originally developed for the purpose of producing the variable density type of record, and is a very accurately responsive device for producing records of that type. -The device is equally well adapted, however, to function according to the present invention' to produce an extremely accurate and undistorted variable width record, of either the known single-serratededge type, or of an improved double-serrated-edge-type first provided vby the present invention. The specic doubleserra-ted-edge record has certain features of improvement as regards accuracy of reproduction, increased volume without distortion, etc., which willappear later.

192s. serial No. 347,886.

While the invention is to be hereinafter illustrated and described particularly in con- -nection with the specific light valve above referred to, it will be recognized that other light valve devices may be found suitable and may be substituted if desired.

y .With this preliminary discussion-in mind, the invention will best'be understood from the following detailed description of present preferred means for carrying the invention into effect, reference for this purpose being had to the accompanying drawings, in which:

Fig. 1 is a diagrammatic view of a system embodying my invention;

Fig. 2 is an interior elevation of the front pole piece assembly of the preferred light valve, showing the light-valve ribbon and lifglliit-slit, this view being taken on line 2-2 o i 1; i

Figi?r 2a is a similar view of a modified light valve adapted to produce the single-serratededge type of record;

Fig. 3 shows the negative double-serratededge sound record obtained in the system 75 of 13Fig. 1, -using the light valve illustrated in ig.2; w L,

Fig.. 4 shows a positive of the negative rec-A ord shown in Fig. 3;

Fig. 5 shows a negative single-serrated- 80 edge record obtained with the use of the light valve shownin Fig. 2a; L

Fig. 6 shows a positive of the negative record illustrated in Fig. 5;

the relations of the light valve aperture and image thereof to the film in a well known prior sound recording system utilizing the specific light valve included in the preferred embodiment of the present invention; and

Figs. 9 -and 10 indicate diagrammatically the relations of thelight valve aperture and image thereof ltothe lilm according tothe present invention.'

In Fig. 2 is shownan interior elevation 95 of the front pole piece assembly of a ty ical well known type of light valve, the ht valve being generally indicated at L in Bgig. 1. This assembly includes an iron late 10 whichforms a part of the core 11 o a mag- 100 netic field winding 12 (see Fig. 1), and also serves as a base for light valve elements now to be described. A pair of opposed capstan' screws 13 are mounted at one end of plate 10, and wound`upon the ends of 'these screws are the ends of a loop 14 of metallic ribbon, the looped end ofwhich is supported at the other end of plate 10 by means of a spring-held pulley 15 mounted thereupon. The ribbon may be tensed to a natural frequency of approximately 7 ,000 vibrations per second. The central portion 14a of the loop is supported by a pair of spaced insulating bridges 17 secured to plate 10, and having notches 18 which space the adjacent edges of the loop normally at a distance of about 2 mils. Plate 10 is provided with a raised pole piece 20, the upper face 21 of which is spaced just below the central portion 14a of the metallic loop. A tapered light slot 22 is provided through pole piece 20 and plate 10 (see Fig. 1), and opens in pole piece face 21 to form a slit 25 parallel to` and just below loop 14. In the present instance this slit is made 8 mils wide. The loop normally covers the two sides of the slit, thereby reducing the light opening to a normal slit 2 mils in width.

In operation, field winding 12 is energized by a constant direct current, and a strong magnetic field exists between pole piece 20 and an opposed pole piece provided on core 1.1, as indicated at 26 in-Fig. 1. A modulated electrical current passed through the metal loop 14 causes the sides of the loop to be vibrated or bowed in and out due to electro-magnetic action with the magnetic field. The sides of the loop are thus caused to open and close, thereb varying the horizontal dimension of the light opening or slit of the valve in accordance with the pulsations of the sound-modulated current.

The light valve as now described has commonly been used to make a variable density record by moving a sensitized film transversely to the light valve loop and slit, and forming an image of the light valve slit transversely on the film. In Fig. 7 the light valve slit is indicated at P, the letter W indicating the constant dimension and the letter D indicating the variable dimension thereof. According to this prior system, the film, indicated at F, is moved transversely to the slit as diagrammed. In Fig. 8 is shown the image P of the slit which is formed upon the film. It is to be noted that the slit image is positioned with its sides of constant dimensionv W transverse to the direction of film movement, and with its sides of variable dimension D in the direction of film movement.

The resulting record is, of course, of the well known constant width, variable density type.

According to the present invention, as distinguished from the system just described, the film is moved in the same direction as the light valve loop `and slit. In Fig. 9 the light lsharply the upper and valve slit is again'indicated at P, the latter W indicating the constant dimension and thc letter D indicating the variable dimension thereof.` But in this case the film, indicated at F, is moved in the direction of the slit. In Fig. 10 is shown the image p of the slit which is formed upon the film, w representing the constant dimension and Z the variable dimension thereof. In this case the dimension w is compressed relatively to the dimension (l, the reason for which being set out later. It is to be noted that in the present case the slit image is positioned with its sides of variable dimension d transverse to the direction of film movement, and with its sides of constant dimension w in the direction of film movement. rThis arrangement, as may readily be seen, will produce a record of variable width.

The light valve is understood to be situated in the system of Fig. 1 with its loop 14 extending vertically, the action being that the horizontally vibratory vertical loop varies the horizontal width of the vertically extending slit of the valve. In Fig. 1 the letter H represents a lamp house, and C a condenser which is adapted to throw light therefrom upon the light valve loop through a tapered light slot 29 provided in the central portion of core 11. An objective O located before the slit, is proportioned and relatively positioned to form a relatively large image thereof in the plane of the vertically moving film F, which film may be driven by any well known means that will impart a constant forward motion thereto. A planocylindrie lens T is preferably placed between objective O and film F, and is situated with its plane face toward the objective, and with the axis of its cylindric surface horizontalthat is, at right angles to the direction of the light valve slit. Duc to the characteristic of the plano-cylindric lens the image of the light valve slit is fiattened or compressed vertically in its constant dimension w, thereby concentrating the light rays and intensifying the image, while the horizontal dimension d of the image remains of good size, being preferably one-tenth of an inch when the light valve slit is modulated at full amplitude.

There is preferably placed before film F a vertical plate A having a relatively narrow horizontal slit S in the path of the light rays, the function of this slit being to define lower edges of the image formed r pon the film. It will be noted, upon consideration, that with the use of this slit it is not necessary to have the light valve slit of any definite length.

It may be seen that there is formed on the film transversely to its direction of movement an elongated image of varying length but of constant intensity; and that there is accordingly printed upon the film a record band of variable width and constant density. The resulting negative record is shown in Fig. 3, in'which the sound track is seen to comprise a central opaque band 35, both edges of which are serrated in accordance with the recorded vibrations of the two sides of the light valve loop. This double-serrated-edge opaque band 35 lies in a clear transp-arent field 36. The corresponding positive record, illustrated in Fig. 4, comprises a doubleserrated-edge transparent band 35a, lying in an opaque field 36a. The positive and negative records represent the original sound equally well, and either may be used in reproduction.

A modified light valve arrangement for making a single-serrated-edge record laccording to the present invention is shown in Fig. 2a. In this view, parts corresponding to similar parts in the form shown in Fig. 2 will be designated by like numerals with the subletter a. In this case a single strip 38 of metal ribbon is utilized, one end of the ribbon being wound upon the end of a capstan screw 40 mounted at the lower end of the plate, the

' ribbon thence passing over insulating bridges l7a,`which support the ribbon to partially cover light slit 25a of pole piece 20a, and the ribbon being tensed and secured at its other end by passing over a spring-held pulley 15a and then down to be wound upon a capstan screw 41 mounted at the upper end of plate 10. It will readily be understood that with this light valve arrangement situated in the system of Fig. 1, the image cast upon film F will have one straight edge representing the uncovered edge of slit 25a, and one varying edge Vrepresenting the vibrating light valve ribbon 38. The resulting negativerecord, shown in Fig. 5, is comprised of an opaque band having one straight and one serrated edge, lyingin a transparent field 46. The positive record, of course, is the photographic reverse, as shown at 45aA and 46a in Fig. 6. Either the positive or negative is a suitable record for reproduction, as before.

Although the invention has been illustrated with specific forms of light valves, it will be understood that any other suitable light valve adapted to vary a linear dimension of a-light slit under sound-modulated current actuation may be substituted, if desired.

It may ,now be seen that I have provided a system by which extremely accurate and undistorted records of the variable width type may be produced. And I have further provided a system for making a record of this general type having specifically a doubleserrated edge, with the accompanying' advantagesliereinbefore referred to.

It will be recognized that the illustrative system specifically described herein is capable of considerable modification and rearrangement without departing from the spirit and scope of my invention; and it is therefore to be understood that the following claims embrace all such modifications and equivalent arrangements as may fairly be construed to fall within the scope of my invention.

I claim: f

1. In a sound recording system, the combination of means forming a substantially rectilinear light aperture, sound-actuated means for varying alinear dimension of said aperture, means for illuminating said aperture, means for movin a sensitized film, an optical system adapted5 to form in the plane of said moving film, an image of said aperture with its varying dimension transverse to the direction of film movement, and an aperture plate having a relatively narrow slit in said optical system adapted to restrict the light rays reaching the film to form an image having a dimension in the direction of film movement relatively narrow as compared with its dimension transverse to the direction of film movement. n

2. In a sound rrecording system, the combination of means forming a substantially rectilinear light aperture, sound-actuated means for varying a linear dimension of said aperture, means for illuminating said aperture, means for moving a sensitized film, an

optical system adapted to form in the plane of said moving film an image of said aperture with its varying dimension transverse to the direction of film movement, and means for restricting the dimensions of the image in the direction of film movement to a dimension less than the normal image in a direction transverse to the direction of film movement.

3. In a sound recording system, the combination of means forming a substantially rectilinear light aperture, sound-actuated means for varying a linear dimension of said aperture, the other linear dimension thereof remaining constant, means for illuminating said aperture, means for moving a sensitized film, and an optical system adapted to form in the plane ofsaid moving film an aperture image relatively compressed in its constant linear dimension, and with its varying dimension transverse to the direction of film movement.

4. In a sound recording system, the combination of means forming a substantially rectilinear light aperture, sound-actuated means for varying a linear dimension of said aperture, the other linear dimension thereof remaining constant, means for illuminating said. aperture, means for moving a sensitized film, an opticalsystem adapted to form in the plane of said moving film an aperture image relatively compressed in its constant linear `dimension and with its varying-dimension small dimension in the direction of film movement.

5. In a sound recording system, the combination of means forming a substantially rectilinear light aperture, sound-actuated means for varying a linear dimension of said aperture, the other linear dimension thereof remaining constant, means for illuminating said aperture, means for moving a sensitized film, and an optical system including an objective and a cylindric lens adapted to Jform in the plane of said moving film an aperture image relatively compressed in its constant linear dimension, and with its varying dimension transverse to the direction of film movement.

6. In a sound recording system, the combination of means forming a substantially rectilinear light aperture, sound-actuated means for varying a linear dimension of said aperture, the other linear dimension thereof remaining constant, means for illuminatin said aperture, means for moving a sensitize film, an optical system including anobjective and a cylindric lens adapted to form in the plane of said moving film an aperture image relatively compressed 1n its constant linear dimension and with its varying dimension transverse to the direction of iilm movef ment, and an aperture plate having a narrow slit in said optical system adapted to restrict y the image formed on the film to a relatively small dimension in the direction of film movement.

7. In a sound recording system, Vthe combination of means forming an elongated light slit, means to move a light-sensitive film in a direction lengthwise of the light slit, soundactuated means for varying the narrower dimension of the light slit, means to proj ect an image of the light slit on the film, and means to restrict said image on the film to a relatively small dimension in the direction of film movement.

8. In a sound recording system, the combination of means forming an elongated light slit, means to move a light-sensitive iilm in a direction lengthwise of the light slit, soundactuated means :for varying the width of the light slit, and optical means for projecting an image of the light slit on the film, said optical means including means to restrict said image on the iilm to a relatively small dimension in the direction of film movement.

9. In a sound recording system, the com`- bination of means forming an elongated light slit, means to Imove a light-sensitive iilm in a. direction lengthwise of the lightslit, sound- 'actuated means for varying the width of the light slit, and optical means for projecting an image of the light slit on the film, said optical means including means for relatively compressing the image Ain the direction'of film movement.

10. In a sound recording system, the combination of means forming an elongated light slit, means to move alight-sensitive film in a direction lengthwise of the light slit, soundactuated means for varying the width of the light slit, and optical ymeans for projecting an image of the light slit on the film, said optical means including means for relatively compressing the image in the direction of iilm movement to a dimension less than the normal image dimension in the direction tfransverse of the film movement.

11. The method of sound recording that includes varying one linear dimension only of a light slot by sound wave actuation, and projecting an image of the light slot onto a movingilight-sensitive iilm with the varying dimensions of the image transverse to the direction of film movement and relatively compressing said image in its dimension in the direction of film movement.

12. The method of sound recording that includes, varying the narrower dimension of an elongated light slot by sound wave actuation, and projecting an image of the light slot onto a light-sensitive lm moving in the direction of elongation of the light slot, with the varying dimension of the image transverse to the direction of filmv movement.

In witness that I claim the foregoing I have hereunto subscribed my name this 21st day of February, 1929.

ROY J. POMEROY. 

